It looks like "xfce4-popup-applicationsmenu" is a simple wrapper Bash
script.
All it does is trying to execute "xfce4-panel" with a long line of
parameters and if that fails, fallback to execute "xfdesktop --menu"
instead.
Man page for "xfce4-panel" doesn't explain anything about
"--plugin-event" parameter, so it looks like it was reworked somehow.
The problem is that "xfce4-panel" never fails to execute with that
undocumented parameter, so fallback option doesn't work.
You can file a bug report about this, or change a command, assigned to
'Alt+F1' key combination, to
"/usr/bin/xfce4-panel --plugin-event=applicationsmenu:popup"
--
With kindest regards, Alexander.
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